Experimental shoulder testing under in-vivo anatomy and physiology

Abstract

Simulating arm abduction using a n experimental shoulder simulator which matches physiological conditions would be of highest interest in shoulder bio-mechanics, e.g. to study the influence of shoulder anomalies on joint reaction force and muscular activity levels, to simulate rotator cuff tears to analyse different surgical treatment approaches, or to investigate primary stability of newly developed implants. For this purpose, we developed an experimental shoulder simulator. However, previous conducted studies revealed that the increase of the joint reaction force while abduction is considerably decreased compared to in vivo measurements, and cranial subluxation was already observed at very low shear reaction force levels. We therefore advanced the existing shoulder simulator by adapting anatomy and physiology to in vivo human shoulder condition by tilting the force action line of the rotator cuff muscles according to anatomical observations 15° caudally, and introduced primary antagonists: the Pectoralis Major and Latissimus Dorsi. The aim of this study was to compare compressive joint reaction force to literature data, to introduce a novel approach to study humeral head migration to detect cranial subluxation, and to analyse maximum shear joint reaction force of stable shoulders